Syria's Interior Minister Ghazi Kanaan has committed suicide, the official news agency in Damascus says.
Kanaan (left) was Syria's top official in Lebanon for years
He was reportedly questioned by a UN investigator last month over the murder of ex-Lebanese PM Rafik Hariri.
For many years Kanaan was Syria's powerful intelligence chief in Lebanon, which was dominated by Syria until its military withdrawal earlier this year.
Hours before his death, he gave what he called his "last" interview, saying he had served Lebanon with honesty.
Mr Kanaan's chief aide said that he had shot himself in the mouth at his office in the interior ministry.
"Gen Kanaan left his office to go home, then he came back after three quarters of an hour, took a gun from the drawer and fired a bullet into his mouth," General Walid Abaza told the AFP news agency.
The authorities are carrying out the "necessary investigation" into the incident, the official Syrian Arab News Agency said.
Earlier, Kanaan contacted a morning broadcast of Voice of Lebanon radio station to give what he called his "last statement".
"We served Lebanon's interests honourably and sincerely... We exerted joint efforts and spared no blood and this resulted in the liberation of Lebanon at a time that it was impossible to do so without Syria," he said.
He asked for his comments to be passed to other broadcast media in Lebanon.
Kanaan served as Syria's top security official in Beirut from 1982. Correspondents say Lebanese leaders had to report to directly on political and security issues.
In 2002 he returned to Damascus as political intelligence chief in 2002, and he joined the cabinet in 2004.
Many will now suspect that Kanaan was a sacrificial lamb, conveniently eliminated before the release of the UN report into Hariri's death, says BBC Middle East analyst Roger Hardy.
The UN report on Hariri's assassination is expected to be published before the end of October.
Correspondents say it is likely to implicate Syria's intelligence regime and its allies in Lebanon in the bombing, that killed 20 people in central Beirut in February.
Damascus has denied any involvement in the Hariri bombing, but it immediately came under heavy international pressure to relinquish its political and military control on Lebanon.
GHAZI KANAAN, 1942 - 2005
Born in 1942 into Allawite minority in Lattakia area, Syria
Graduated from military school in 1965
Served as aide to late President Hafez al-Assad in early 1970s
Syrian spy and security chief in Lebanon from 1982 to 2002
Appointed head of political security in Damascus in 2002
Appointed Syrian interior minister in 2004
Assets frozen by US treasury in early 2005
Syrian President Bashar al-Assad told the CNN television station that he was not aware of any evidence to suggest his country had a hand in Hariri's death.
"If indeed there is a Syrian national implicated in it, he would be considered a traitor and most severely punished," Mr Assad said.
The interview was recorded before news of Kanaan's death became public.
The UN investigator, German prosecutor Detlev Mehlis, questioned Kanaan and six other Syrian officials in Damascus during a visit at the end of September, Lebanese media reported.
The United States froze his assets there in July saying he had aided terrorism in Lebanon.